Infants with single ventricle (SV) congenital heart disease (CHD) frequently encounter feeding difficulties, placing them at risk for growth failure and increased morbidity and mortality. The purpose of this study is to examine the physiologic changes that infants with SV CHD experience with three different feeding methods, specifically breastfeeding, bottle feeding with a standard-flow nipple, and bottle feeding with a low-flow nipple. Understanding how variations in feeding method affect physiology will enable the development of evidence-based feeding strategies to improve feeding outcomes and support growth. Specific aims of the study are to: (1) examine the physiologic state changes (heart rate and oxygen saturation) and observational indicators of distress (behavioral disorganization, swallowing dysfunction, and respiratory dysregulation) with the three feeding methods and (2) explore the contribution of heart rate variability to our understanding of physiologic state prior to feeding, during feeding, and in the recovery period after feeding with the three feeding methods. A single subject design study with replication in six subjects is proposed where each subject will receive three feedings; one of each feeding condition. Prior to the study, a pilot study will be performed in which one infant will receive the same feeding protocol; one of each condition. Thus, the complete study will involve a total of seven subjects. For each subject, twelve hours of data will be collected using standard heart rate and oxygen saturation equipment, as well as videotaping of behavior. This design allows for a relatively small sample, which is necessary given the rarity of the diagnosis, while observing all possible permutations of the three feeding conditions and providing adequate data to meet the aims of the study. The study purpose is aligned with the missions of the National Institute of Nursing Research to improve the quality of life of patients, integrate biological and behavioral science, and generate new technologies. The information to be obtained has the potential to promote the health of infants with SV CHD, improving the quality of life of both infants and their families. The methods proposed integrate the study of physiology and behavior and use an innovative technique, heart rate variability, to better understand the phenomenon under study. This is a study of feeding in infants who are born with complex heart defects. The goal is to better understand what happens to these children when they are breastfed or fed using two different bottle nipples that offer different rates of milk flow. The knowledge gained will be used to develop more appropriate feeding strategies for these vulnerable infants so they can achieve better growth and avoid complications.